1. Field of the Invention
The present invention relates to a circuit arrangement for the coarse protection against surge voltages for an intermediate repeater or regenerative repeater of a communications installation, comprising a coaxial length of cable which is provided at the input and at the output with a current supply separating filter, respectively, and, at the input and/or at the output is provided with a device containing a surge voltage arrester for the purpose of coarse protection against surge voltages in the case of surge voltage influencing on the length of cable, whereby the current supply separating filters, which are provided for the purpose of remote feeding via a remote feed current path including the inner conductor of the coaxial cable, respectively contain an inductor arrangement, and whereby the remote feed current path extends via the inductor arrangements of the current supply separating filters and the feed input therebetween of the intermediate repeater or regenerative repeater, and whereby the outer conductor of the incoming cable and the outer conductor of the outgoing cable are interconnected by way of a cable outer conductor connection of the coaxial length of cable.
2. Description of the Prior Art
A circuit arrangement of the type generally set forth above is already known from the Austrian Letters Patent No. 5 20 220.
In the case of the known circuit arrangement, the inner conductor and the outer conductor of the incoming coaxial cable are directly connected to the input of the intermediate repeater via a surge voltage arrester in order to protect the intermediate repeater against arcings. In the case of response of the surge voltage arrester, a steep voltage jump occurs, which, attenuated by the pre-equalizer but, acts on the input of the repeater. In the case of regenerators which transmit very broadband signals, however, such an attenuation is not available. In this case, a corresponding design of the fine protection against surge voltages and of the active regenerator portion is then necessary.
In the case of the known circuit arrangement, a capacitor connects the one connection of a feed input with the outer cable conductor connection. The capacitor must have a low impedance for high frequencies in order to avoid a high-frequency feedback from the output of the repeater to the input. Therefore, the surge voltage arrester, in terms of high frequency, i.e. for the frequencies contained in the steep switching edge of the surge voltage arrester, is connected in parallel with the inductor located in the remote feed current path, so that a high-frequency noise pulse generated by the surge voltage arrester is input-coupled via the high-pass filter located at the repeater input into the equalizer provided at the input.
From W. Peters: "Current Supply Separating Filters for Remotely Fed Carrier Frequency Intermediate Repeaters", Frequency 28 (1974), pp. 326-333, particularly Page 327, illustration 2C1, current supply separating filters are already known which contain a low pass filter in order to increase the circulatory attenuation. In this connection, the term circulatory attenuation is intended to denote the attenuation between the output pair of terminals and the input pair of terminals of the repeater. From Page 328, illustration 4, a so-called potential separating filter having line inductors is apparent. In the case of line inductors the two windings are a very low resistance to the oppositely-flowing signal current. A very high resistance is offered the current flowing only through one winding, respectively. The illustrations 15E and 15F on Page 332 show coaxially-constructed potential separating filters.
From U.S. Pat. No. 4,467,472, fully incorporated herein by this reference, a frequency separating filter is already known in which the outer conductor of a homogeneous line is connected with the inner conductor of a heterogenous line. The connection, adjacent a connection cable, of the outer conductor of the hetergenous line is connected to the shield, the other connection is connected with the reference potential of the active regenerator portion.
The surge voltages which occur in the case of surge voltage influence on lengths of coaxial cable, generally have comparatively great rise times in the microsecond range and pulse durations on the order of magnitude of one more second. The rise time and the pulse duration of digital signals of a high-bit rate lies in the nanosecond range. It follows therefrom that the current supply separating filters of the regenerative repeaters, which are designed for the transmission of the high-frequency useful pulses, exhibit a great attenuation of low-frequency noise pulses from the cable. Surge voltage pulses having flat edges in the microsecond range are virtually completely deflected at the current supply separating filters. Examinations within the scope of the present invention have shown that the fine protection against surge voltages in these instances need not take up any energy as long as the amplitude of the surge voltage pulses lies below their minimum operating voltage of the arresters.
However, the surge voltage arrester can, upon responding, generate voltage jumps having very steep edges. In order that the noise pulses therefore coupled in can be taken up by the fine protection circuits against surge voltages, e.g. current limiting resistances with relatively great dimensions and protective diodes having a relatively large crystal surface are necessary. This necessitates a large self-inductance of the resistances and a large self-capacitance of the diodes. However, components of this type influence the transmission properties of the fine protection against surge voltages for the digital signals in an unfavorable manner, in particular, on the transmitting side, since steep pulses with as great as possible an amplitude must be generated here, which presupposes low parasitic impedances of the components.